1. Field of the Invention
The present invention relates to an actuator device for an optical device that moves an optical member in and out of an optical path using magnetic force, and also to an image-capture apparatus including such an actuator device.
2. Description of the Related Art
An actuator device for an optical device in related art is disclosed in Japanese Unexamined Patent Publication NO. 2004-194403. In Japanese Unexamined Patent Publication NO. 2004-194403, an electro-magnetic actuator configured to generate drive force from electro-magnetic force. Specifically, the electro-magnetic actuator is applied at the time of driving a shutter blade of camera, and the like, and a camera shutter device that employs the electro-magnetic actuator. The electro-magnetic actuator described in Japanese Unexamined Patent Publication NO. 2004-194403 is configured as follows. “This electro-magnetic actuator includes a rotor having an outer circumference divided in a circumferential direction such that each divided portion is polarized into alternately different magnetic polarity and having a drive pin formed in a manner protruding from the above-described outer circumference, an exciting coil, and a yoke having a circular arc surface facing the outer circumference of the above-described rotor and having a first magnetic polarity portion and a second magnetic polarity portion in which mutually different magnetic polarities are generated by allowing to flow electric current in the above-described coil”. “In this electro-magnetic actuator, the drive force is output from the above-described drive pin by rotating in a prescribed angle range, and the above-described rotor is protruded from the above-described outer circumference to the outside in a radial direction and is polarized into the same magnetic polarity as this outer circumference, and in addition this rotor has projection portions formed in a manner being opposable to the above-described first magnetic polarity portion and the above-described second magnetic polarity portion”.
According to the electro-magnetic actuator having such configuration that is described in Japanese Unexamined Patent Publication NO. 2004-194403, “a surface facing the yoke increases as the whole of rotor since the projection portion is provided which is protruded from the outer circumference of the rotor to the outside in the radius direction while being polarized into the same magnetic polarity as this outer circumference and that is formed in a manner being opposable to the first magnetic polarity portion and second magnetic polarity portion of the yoke”. As a result, there can be expected such an effect “that the electro-magnetic actuator capable of generating desired retaining force and drive torque can be provided while reducing a size of the actuator.
An actuator device using a magnetic force of a magnet has been provided to move an optical member such as a shutter and a fixed diaphragm in an optical device. A plastic magnet having a magnetic powder mixed into plastic, for example, is generally used as the magnet for this actuator device. Since the plastic is used as a major component, this plastic magnet is excellent in formability, however, the generated magnetic force is weak.
Accordingly, a diameter of the plastic magnet may be increased to increase the magnetic force to a prescribed value in the optical device of related art. As a result, the whole optical device increases in size and hence an image-capture apparatus having such optical device also increases in size.
In contrast, a permanent magnet having a neodymium compound and a samarium compound, capable of generating a strong magnetic force, with the magnet being small in size has recently been developed and used.
In this case, the permanent magnet having the neodymium compound and the samarium compound is formed by sintering. Thus, it is preferable that the sintered permanent magnet be formed into a simple shape in view of formability. The simple shape, in this case, implies a cylindrical column since the cylindrical column can easily be manufactured comparatively by sintering.